Impact of Biochar on Soil Moisture0

IBI Research Summary:

Impact of Biochar on Soil Moisture

Updated: 5 February 2010

Authors: Kelpie Wilson and Julie Major, PhD

Note: IBI Research Summaries are intended to provide answers about biochar science for the general public. These summaries are based on IBI’s review of published scientific literature. As this literature is updated, IBI will update these summaries. Please contact IBI at info@biochar-international.org if you have questions or information to share.

Question: Does biochar help soils retain moisture?

More studies, especially field studies, are needed on the question of water retention with biochar, but the results so far consistently show benefits in sandy soils where this function is most needed.

The Australian national science agency, CSIRO, released a comprehensive review (Biochar, climate change and soil: A review to guide further research) of biochar in February 2009, co-authored by Rothamsted Research and Newcastle University in the UK. The CSIRO review looked at work done on biochar impact on soil moisture retention. While it found few studies that directly addressed soil moisture retention with biochar, it found that “Many studies where the effect of biochar on crop yield has been assessed have cited moisture retention as a key factor in the results.”

CSIRO cited a study (Gaskin et al., 2007) that found water retention doubled in a loamy sand soil, and a study of Terra Preta (Glaser et al., 2002) that showed water retention was18% higher than adjacent highly-weathered tropical soil.

In a laboratory study by Novak et al. (2009), where different biochar types were added to a loamy sand, biochar either had no significant effect or increased the water holding capacity of the soil. Chan et al (2007) obtained similar results working with a hardsetting Australian soil, with pot trials. Asai et al. (2009) applied biochar to field soil cropped to upland rice at several locations in Laos, and found improved surface infiltration of water.

Also in the field, Major et al. (2009) found that biochar application to a clayey savanna soil of Colombia increased surface water infiltration. Although infiltration is different from moisture holding capacity, if more moisture enters the soil during rain events, more can then potentially be retained by soil.

A case study in Ghana illustrates the significance of biochar augmented water retention in a dryland crop: